Magnetic tape cartridge and recorder/reproducer a magnetic tape cartridge

ABSTRACT

A magnetic tape cartridge and A magnetic tape cartridge recording/reproducing apparatus, which can prevent a magnetic tape from being charged to avoid damage of a magnetic head while lowering the resistance of the magnetic tape and maintaining optimum electromagnetic conversion properties. A tape reel ( 7 ) is formed from a conductive material, and one end portion of a magnetic tape ( 6 ) connected to a reel hub ( 7 B) has a surface resistivity [Ω/sq] in the order of 10 7  or less. In the magnetic tape ( 6 ) having a multilayer structure which comprises a magnetic layer ( 23 ), a nonmagnetic conductor layer ( 22 ), a plastic film ( 21 ), and a back coat layer ( 24 ) from the magnetic surface ( 6 M) side, even when the surface resistivity of the magnetic layer ( 23 ) exceeds 10 7  Ω/sq, the magnetic layer ( 23 ) is removed and the exposed nonmagnetic conductor layer ( 22 ) is connected to the reel hub ( 7 A), thus lowering the resistance of the magnetic tape while maintaining optimum electromagnetic conversion properties.

TECHNICAL FIELD

The present invention relates to a magnetic tape cartridge and amagnetic tape cartridge recording/reproducing apparatus, which prevent amagnetic head from suffering damage due to electrostatic discharge ofcharges accumulated on a magnetic tape.

BACKGROUND ART

Conventionally, in the field of electronic computers, as their size isreduced and the throughput speed increases, there are increasing demandfor magnetic disk apparatuses and other external recording apparatuseswherein they should have higher recording density and higher accessspeed. Especially in the magnetic disk unit, as the recording density isimproved, the recording bit is reduced, and therefore there is a problemin that the output in reproduction by a magnetic head is lowered. Forsolving this problem, differing from a conventional apparatus usingsolely one electromagnetic induction type head for use both in recordingand reproduction, a recording/reproducing apparatus using a recordinghead and a reproducing head which are separately provided, namely, usingan electromagnetic induction type head for recording and an MR head(magneto-resistive head) for reproduction utilizing a magnetoresistanceeffect is developed.

The MR heads are roughly classified into AMR (anisotropicmagneto-resistance) heads utilizing anisotropic magnetoresistance effectand GMR (giant magneto-resistance) heads utilizing giantmagnetoresistance effect. Particularly, the GMR head can realizerecording with a density as high as 3 gigabits or more per 1 squareinch, and hence the GMR head is mainly used in the field of magneticdisk.

On the other hand, the AMR heads are introduced into magnetic tapecartridge of a single reel type, typically, for example, a DLT (digitallinear tape) or LTO (linear tape open format cartridge) and used forreproduction of a recording/reproducing system for magnetic tape. Fromthe technical changes of a hard disk (HD), it is expected that the GMRhead will replace the AMR heads in the near future to become the mainforce in magnetic tape systems.

However, when the GMR head is introduced as a reproducing head in themagnetic tape system, a problem of prevention of ESD (electrostaticdischarge) is encountered as a technical issue to be solved.

The ESD prevention is more severe in the GMR head than that in the AMRhead, and ESD even at a level that causes no problem in the AMR head canbe at a charge level sufficient to break the spin valve elementconstituting the GMR head. Of course, in the AMR head, the cartridge ormagnetic tape may be charged to an excessive amount during a long-termstorage or actual use, and the ESD level is required to be lowered fromthe viewpoint of reliability, although that not constituting a seriousproblem.

In conventional HD applications, the magnetic head is basically putabove the magnetic disk so as not to be directly in contact with themagnetic disk, and the HD is operated only in a grounded housing tosatisfactorily ground both the magnetic disk and the magnetic head, thuspreventing ESD.

On the other hand, the magnetic tape system is basically removable, and,in jukebox type library using a robotics operation, an action of drawinga cassette is inevitable, and therefore, not only is a possibility ofESD even higher than that of the HD, but also a danger of ESD isconsiderably high when the use environment is at a low humidity. Fromthis point of view, in the GMR heads in general, or in the AMR headsdepending on the actual use environment and time, the high densitymagnetic recording tape system can in principle have arecording/reproducing density equivalent to that of the HD, but itcannot be satisfactorily realized in the actual application due to theproblem of ESD.

In order to solve the above mentioned problems, a method of improvingthe circuit to prevent ESD is considered as disclosed in ExaminedJapanese Patent Application Publication No. H07-92718, for example, butit is still not possible to obtain a structure which surely enablesdrain of electrical charges when the magnetic tape and the head operateboth in a moving state. On the other hand, for lowering the electricresistance of a coating type magnetic film, an attempt to add conductivecarbon black is made, but, not only does the addition of a nonmagneticmaterial, which is not a magnetic material, lower the electromagneticconversion properties, but also the resistance value is roughlycontrolled, and therefore this is not suitable for control of theperformance with high yield.

A medium, such as a tape of a deposited type, has a structure such thatthe metallic film is inevitably in contact with the MR Head, and hencehas in principle a considerably reduced resistance. However, from theviewpoint of the mobility of charges, the electric resistance of themedium is too low, and, when static electricity is generated at acertain point in time, charges move toward the head having the lowestresistance, so that the spin valve element of the GMR head is easilybroken.

In view of the above problems, the present invention has been made, andan issue is to provide a magnetic tape cartridge and an apparatus forrecording/reproducing the same, which can prevent the magnetic tape frombeing charged to avoid damage of the magnetic head while lowering theresistance of the magnetic tape and maintaining optimum electromagneticconversion properties.

DISCLOSURE OF THE INVENTION

The present inventors have made devote efforts with a view towardsolving the above-mentioned problems and, as a result, it has been foundthat, by lowering the electric resistance of the magnetic tape andgrounding the magnetic tape to prevent the magnetic tape from beingcharged, electrostatic discharge damage of the magnetic head, especiallythe magnetic head constituted by an MR element is avoided, and thepresent invention has been completed.

Specifically, a magnetic tape cartridge of the present invention ischaracterized in that the reel hub is formed from a conductive materialand one end portion of the magnetic tape connected to the reel hub has asurface resistivity [Ω/sq] in the order of 10⁷ or less. The reel hubformed from a conductive material is electrically connected to the reeldrive shaft upon loading the tape, and hence, the reel drive shaft iselectrically grounded to prevent the magnetic tape from being charged.In this construction, it is necessary that at least the surface of thereel drive shaft be constituted by a conductive material, such as ametal, and the electric resistance [Ω] of from the reel hub as a groundterminal to the ground (hereinafter, referred to as “ground resistance”)be in the order of 10⁷ or less.

The wording “in the order of 10⁷” used here means values represented byn×10⁷ wherein n is a number of 1 to less than 10. Accordingly, thewording “in the order of 10⁷ or less” means values less than 1×10⁸.These wordings used in the claims and descriptions below have the samemeanings.

In addition, another magnetic tape cartridge of the present invention ischaracterized in that the cartridge body is formed from a conductivematerial, and the magnetic tape has surfaces individually having asurface resistivity [Ω/sq] in the order of 10⁷ or less and the magnetictape is electrically connected to the cartridge body. The electricalconnection between the cartridge body and the magnetic tape is made byproviding, for example, a conductive arm member between the inner wallof the cartridge body and the magnetic tape, enabling drain ofelectrical charges on the magnetic tape toward the cartridge body side.In this case, the cartridge body is electrically grounded to prevent themagnetic tape and cartridge body from being charged. In this case, it isnecessary that the electric resistance [Ω] of from the arm member as aground terminal to the ground (hereinafter, referred to as “groundresistance”) be in the order of 10⁷ or less.

Further, A magnetic tape cartridge recording/reproducing apparatus ofthe present invention is characterized in that it includes at least amagnetic head for recording information on a magnetic tape orreproducing information recorded on the magnetic tape, and a pluralityof guide rollers for guiding the traveling magnetic tape, wherein atleast one of the guide rollers is electrically grounded, and wherein thetraveling surface of the magnetic tape in contact with the groundedguide roller has a surface resistivity [Ω/sq] in the order of 10⁷ orless. This construction prevents the magnetic tape, which travels whilebeing in contact with the guide rollers, from being charged. In thiscase, it is necessary that the electric resistance [Ω] of from the guideroller as a ground terminal to the ground (hereinafter, referred to as“ground resistance”) be in the order of 10⁷ or less.

For lowering the electric resistance of the magnetic tape, especiallythe electric resistance on the magnetic surface side without loweringthe electromagnetic conversion efficiency, it is preferred that themagnetic tape includes a nonmagnetic conductor layer constituted by anonmagnetic conductive material disposed between a plastic film and amagnetic layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing whole of a magnetic tape cartridgeaccording to the embodiment of the present invention.

FIG. 2 is an exploded perspective view of a magnetic tape cartridgeaccording to the embodiment of the present invention.

FIG. 3 is a plan view of the inside construction of a magnetic tapecartridge according to the embodiment of the present invention as viewedfrom the lower half side.

FIG. 4 is a cross-sectional view showing the construction of a magnetictape applied to the first embodiment of the present invention.

FIGS. 58(A) and (B) are perspective views diagrammatically showing theconnection portion between a magnetic tape and a tape reel applied tothe embodiment of the present invention, wherein FIG. 5 (A) shows a modein which the magnetic tape is fixed so that the magnetic surface side ofthe magnetic tape is in contact with the reel hub, and FIG. 5 (B) showsa mode in which the magnetic tape is fixed so that the back surface sideof the magnetic tape is in contact with the reel hub.

FIG. 6 is a cross-sectional view diagrammatically showing the action ofa magnetic tape cartridge according to the first embodiment of thepresent invention.

FIG. 7 is a plan view of the inside of an upper half of a magnetic tapecartridge according to the second embodiment of the present invention.

FIG. 8 is a perspective view of an essential portion of FIG. 7.

FIG. 9 is a view for illustrating a ground mode of the magnetic tapecartridge according to the second embodiment of the present invention.

FIG. 10 is a plan view of the inside of an upper half of a magnetic tapecartridge according to the third embodiment of the present invention.

FIG. 11 is a perspective view showing a magnetic tape cartridge and arecording/reproducing apparatus according to the forth embodiment of thepresent invention.

FIG. 12 is a diagrammatic view showing an essential portion of therecording/reproducing apparatus according to the forth embodiment of thepresent invention.

FIG. 13A to 13B are diagrammatic views showing examples of variations ofthe forth embodiment of the present invention, wherein FIG. 13A shows anexample of the construction in which a magnetic tape travels so that themagnetic surface of the magnetic tape is in contact with the guiderollers immediately behind and immediately ahead of the magnetic head,FIG. 13B shows an example of the construction in which a magnetic tapetravels so that the magnetic surface of the magnetic tape is in contactwith the guide roller immediately behind the magnetic head, and FIG. 13Cshows an example of the construction in which a magnetic tape travels sothat the magnetic surface of the magnetic tape is in contact with theguide roller immediately ahead of the magnetic head.

FIG. 14 is a diagrammatic view showing the element structure of a GMRhead used in the Examples according to the preferred embodiments of thepresent invention.

FIG. 15 is a cross-sectional view of an essential portion of a magnetictape cartridge, showing an example of variation of the second and thirdembodiments of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings. In the following embodiments, an explanationis made on an example in which the magnetic tape cartridge is applied toa single reel type magnetic tape cartridge (DLT type), typically amagnetic recording medium for use in computer data recorder.

First, the whole construction of a magnetic tape cartridge Cl accordingto the present embodiment is described with reference to FIGS. 1 to 3.In FIG. 2, the magnetic tape cartridge C1 is shown upside down.

In the magnetic tape cartridge C1, an upper half 1 and a lower half 2constituted by, for example, a composite material of polycarbonate andglass fiber are bonded together to form a cartridge body 3, and a singletape reel 7 having a disc-form upper flange 4 and lower flange 5 ishoused in the cartridge body 3 so that it is capable of rotating.

In the tape reel 7, a magnetic tape 6 having a leader tape 9 connectedto its one end is wound round a reel hub provided on the upper flange 4so that the magnetic surface of the magnetic tape is arranged on theinner side. The tape reel 7 has a ring-form bearing which is pressed andfixed into a circular recess portion formed in the center portion of theupper flange 4, and the tape reel rotates by a not shown reel rotatingshaft fitted to the bearing. In addition, one end of the tape reel 7 isin contact with an inner surface la of the upper half 1, and another endis always pressed to the lower half 2 side by a reel spring 8 which isin contact with the reel rotating shaft. The reel spring 8 isconstituted by a compression coiled spring in a cylindrical form.

In the magnetic tape cartridge C1 which is not set in arecording/reproducing apparatus, namely, upon being unused, the tapereel 7 cannot rotate due to a pair of brake members 12, 13 pressed bytorsion springs 10, 11. Specifically, the tape reel 7 cannot rotate dueto mating portions 15, 16 which are formed on, respectively, the brakemembers 12, 13, and which mate with a gear portion 14 formed on theouter periphery of the upper flange 4. The torsion springs 10, 11 andthe brake members 12, 13 are rotatably fitted to, respectively,supporting shafts 26, 27 provided on the inner surface 1 a of the upperhalf 1.

In addition, upon being unused, the magnetic tape 6 is completely woundround the tape reel 7, and the leader tape 9 is hooked by a hook 17provided on the side of a front face 3 a of the cartridge body 3. Anopening portion 34 through which the magnetic tape 6 is drawn out of thecartridge body 3 is in a closed state by a switching door 18 which isrotatably fitted to a shaft 20.

On the other hand, in the magnetic tape cartridge C1 which is set in arecording/reproducing apparatus, namely, upon being used, when a reelstand on the recording/reproducing apparatus side rises, the tape reel 7repels the force of the reel spring 8 to be brought up to the centerportion of the cartridge body 3 and reel unlock plugs on therecording/reproducing apparatus side are inserted into reel unlock holes35A, 35B to unlock the brake members 12, 13, thus enabling the tape reel7 to rotate. Further, the switching door 18 is in an open state by adoor switching means provided on the recording/reproducing apparatusside. Further, the magnetic tape 6 is drawn out of the cartridge body 3by a tape drawing means provided on the recording/reproducing apparatusside.

In the magnetic tape cartridge C1, a wrong deletion prevention member 19for preventing wrong recording and wrong deletion on the magnetic tape 6is provided. The wrong deletion prevention member 19 is slidablyprovided on the back surface of the cartridge body 3 which is on theopposite side of the switching door 18.

Next, the construction of the magnetic tape 6 in the present embodimentis described.

FIG. 4 is a cross-sectional view showing the construction of themagnetic tape 6. In the magnetic tape 6 in the present embodiment, amagnetic layer 23 is formed on the surface of a plastic film 21 througha nonmagnetic conductor layer 22 constituted by a nonmagnetic conductivematerial, and a back coat layer 24 constituted by a nonmagneticconductive material is formed on the back surface of the plastic film21. In the following descriptions, the surface on which the magneticlayer 23 is formed is referred to as “magnetic surface 6M”, and thesurface on which the back coat layer 24 is formed is referred to as“back surface 6B”.

The plastic film 21 has a thickness of 1 to 100 μm, and is formed bymelt or dissolution extrusion of an organic polymer, if necessary,followed by orientation in the longitudinal direction and the widthdirection. Examples of organic polymers include polyolefins, such aspolyethylene and polypropylene, polyesters, such as polyethyleneterephthalate and polyethylene-2, 6-naphthalate, polyamides, vinylchloride, vinylidene chloride, polyvinyl alcohols, aromatic polyamides,and polyamideimides.

As the nonmagnetic conductive material constituting the nonmagneticconductor layer 22 and the back coat layer 24, a nonmagnetic conductivematerial, such as Al, Ti, Si, Cu, Zr, or carbon black, is used. As amethod for forming the nonmagnetic conductor layer 22 and back coatlayer 24 on the top and back surfaces of the plastic film 21, aconventionally known deposition method, such as an application method, aplating method, a vapor deposition method, a sputtering method, or anion plating method, can be used.

The magnetic layer 23 is formed by dispersing ferromagnetic oxidepowder, such as y ferrite, Co-containing γferrite, or chromium oxide, orferromagnetic metallic powder, such as Fe, Co, Ni, Fe-Co, or Fe-Ni, inan organic adhesive, such as a vinyl chloride polymer, an acrylic esterpolymer, or an urethane polymer, and applying the resultant mixture ontothe nonmagnetic conductor layer 22 and curing it.

As mentioned above, in the magnetic tape 6 in the present embodiment, byvirtue of having the nonmagnetic conductor layer 22 and back coat layer24 formed, the electric resistance is lowered while maintaining optimumelectromagnetic conversion properties of the magnetic layer 23, ascompared to that of a magnetic tape in which the nonmagnetic conductorlayer 22 and back coat layer 24 are not formed.

By this construction, the resistance of the magnetic tape 6 is loweredwhile maintaining optimum electromagnetic conversion properties of themagnetic layer 23, so that the magnetic tape 6 can be prevented frombeing charged. However, the magnetic tape 6 merely having thisconstruction has a quasi-capacitor structure, and therefore the magnetictape cartridge C1 disadvantageously serves as a storage for charges whenthe magnetic tape cartridge C1 is not set in a recording/reproducingapparatus, namely, upon being unused. For this reason, when chargestemporarily undergo spark toward the magnetic head during the use of themagnetic tape cartridge C1, the magnetic head suffers fatal damage.

For preventing this, in the present invention, the magnetic tape 6 isgrounded to prevent the magnetic tape 6 from being charged, thusavoiding damage of the magnetic head, especially the magnetic headconstituted by an MR element.

FIRST EMBODIMENT

In the present embodiment, the upper flange 4 (including a reel hub 7A)and lower flange 5 constituting the tape reel 7 is formed from aconductive material, such as a metal or a conductive plastic, and themagnetic tape 6 in the above construction is electrically connected tothe tape reel 7.

With respect to the metal material forming the tape reel 7, there is noparticular limitation, but a metal material having a relatively smallspecific gravity, such as an aluminum, magnesium, or titanium metalmaterial, is preferably used as a constituent material for the tapereel. The conductive plastic means a synthetic resin material, such asPOM or ABS, which contains conductive filler so as to have conductivity.

Here, the conductive filler means filler added for impartingconductivity to a material, and examples include particulate filler,flake filler, and fibrous filler. A representative example ofparticulate filler is conductive carbon, and examples of flake fillerinclude aluminum flake, nickel flake, and nickel coated mica. Examplesof fibrous filler include various fibers of carbon, aluminum, copper,brass, and stainless steel.

The connection of the magnetic tape 6 to the tape reel 7 is made, asdiagrammatically shown in FIG. 5(A) and FIG. 5(B), using aconventionally well known damper 30 for clamping the end portion of themagnetic tape 6 to the reel hub 7A of the tape reel 7 (clamping portionand the like are not shown). The damper 30 is constituted by anonconductive material, such as a synthetic resin material, and disposedso as to face a recess formed in the reel hub 7A and fitted to the reelhub 7A by being mechanically pressed from the back.

The electrical connection between the magnetic tape 6 and the tape reel7 has a mode such that the magnetic surface 6M of the magnetic tape 6 iselectrically connected to the reel hub 7A as shown in FIG. 5(A) and amode such that the back surface 6B of the magnetic tape 6 iselectrically connected to the reel hub 7A as shown in FIG. 5(B). In thepresent embodiment, the contact resistance [Ω] between the magnetic tape6 and the reel hub 7A is in the order of 10⁷ or less.

The mode in which the magnetic surface 6M of the magnetic tape 6 iselectrically connected to the reel hub 7A has a construction such thatthe magnetic layer 23 in the end portion region of the magnetic tape 6is completely or incompletely (so that the magnetic layer 23 partiallyremains) removed to expose the underlying nonmagnetic conductor layer22, and the tape is held by the damper 30 in a state such that theexposed nonmagnetic conductor layer 22 is in contact with the reel hub7A. In the present embodiment, the magnetic layer 23 is removed so thatthe surface resistivity [Ω/sq] of the magnetic surface 6M connected tothe reel hub 7A becomes in the order of 10⁷ or less.

When the surface resistivity of the magnetic layer 23 is in the order of10⁷ or less, that is, the surface resistivity of the magnetic surface 6Mis in the order of 10⁷ or less without removing the magnetic layer 23,the magnetic layer 23 may be directly brought into contact with the reelhub 7A.

On the other hand, the mode in which the back surface 6B of the magnetictape 6 is electrically connected to the tape reel 7A has a constructionsuch that the tape is held by the damper 30 in a state such that theback coat layer 24 of the magnetic tape 6 is in contact with the reelhub 7A. In the present embodiment, the back coat layer 24 is adjusted sothat the surface resistivity [Ω/sq] of the back surface 6B connected tothe reel hub 7A becomes in the order of 10⁷ or less.

When the clamper 30 is formed from a conductive material, such as ametal, both the magnetic surface 6M and the back surface 6B can beconnected to the reel hub 7A in the construction of FIG. 5(A).

By the construction described above, when the magnetic tape cartridge C1is set in a recording/reproducing apparatus, namely, upon being used, asdiagrammatically shown in FIG. 6, a reel drive shaft 33 on therecording/reproducing apparatus side mates with a gear portion 7 a onthe lower plane of the tape reel 7 through a reel shaft insert hole 29formed in the lower plane of the cassette body 3 to drive the tape reel7 to rotate. The reel drive shaft 33 is constituted by a metal material,such as stainless steel, and connected to a ground circuit E1 (groundresistance: 10⁷ Ω or less) using the reel hub 7A as a ground terminal,including the reel drive shaft 33, on the recording/reproducingapparatus side.

In the present embodiment, the magnetic tape 6 is connected through theconductive tape reel 7 to the reel drive shaft 33 electrically grounded,and therefore the magnetic tape 6 is prevented from being charged, and,even when being charged, electrical charges can be surely drainedthrough the tape reel 7 toward the external ground circuit E1 includingthe reel drive shaft 33, so that attack to the magnetic head due tocharges on the magnetic tape 6 is prevented, thus making it possible toavoid electrostatic discharge damage of the magnetic head. Especially inthe recording/reproducing apparatus having as a magnetic head an MR headwhich is very easily affected by static charge, the present invention iseffective.

SECOND EMBODIMENT

FIG. 7 to FIG. 9 show a second embodiment of the present invention. Inthe figures for the second embodiment and those for the above firstembodiment, similar parts or portions are indicated by similar referencenumerals, and the detailed descriptions therefore are omitted.

A magnetic tape cartridge C2 according to the present embodiment has aconstruction in which an upper half 51 and a lower half (not shown) areconstituted by a synthetic resin material having low dischargeproperties, for example, a conductive plastic to impart conductivity toa cartridge body 53.

In the cartridge body 53, there is provided an arm member 40 forelectrically connecting the magnetic surface 6M of the magnetic tape 6having the above-described construction to the inner wall of thecartridge body 53. The arm member 40 is constituted by a metal material,such as an aluminum alloy or stainless steel, or a conductive plastic,and a base portion 41 is electrically and physically connected to, forexample, the inner wall of one side portion of the upper half 51 and anarm edge 42 is in contact with the magnetic layer 23 of the magnetictape 6.

In the connection of the base portion 41 of the arm member 40 to theinner wall of the upper half 51, a conductive adhesive comprising, forexample, an adhesive resin material, such as a silicone resin,containing therein metallic particles can be used. Alternatively, aconstruction in which the base portion 41 of the arm member 40 and theinner wall of the upper half 51 are riveted by means of a metallic rivetcan be applied.

As the contact mode of the arm edge 42 to the magnetic tape 6, from theviewpoint of increasing the contact area between them to lower thecontact resistance, a mode in which the arm edge 42 has an elasticcontact with the magnetic tape 6 at a constant pressure is preferred.

For lowering the frictional resistance between the arm edge 42 and thetraveling magnetic tape 6, the arm edge 42 has a cylindrical formcapable of rotating as shown in FIG. 8, and can rotate while being incontact with the magnetic surface 6M on the inner side of the magnetictape 6. The arm edge 42 is not rotatable and may have merely a shaftform longer than the width of the magnetic tape 6.

By virtue of the arm member 40 having the above construction, theelectrical connection between the magnetic surface 6M of the magnetictape 6 and the cassette body 53 can be easily made. In the presentembodiment, the surface resistivity [Ω/sq] of the magnetic surface 6M ofthe magnetic tape 6 is adjusted to be in the order of 10⁷ or less.

When the magnetic tape cartridge C2 of the present embodiment having theconstruction described above is set in a recording/reproducingapparatus, as shown in FIG. 9, it is housed in a cassette compartment 31in the recording/reproducing apparatus to be aligned in therecording/reproducing apparatus. The cassette compartment 31 isconstituted by a housing made of a metal, such as stainless steel, andthe both sides and front face of the magnetic tape cartridge C2 setthrough an insert hole 32 are respectively supported by inner walls 33a, 33 b, 33 c to align the magnetic tape cartridge C2.

The cassette compartment 31 is connected to a ground circuit E2 on therecording/reproducing apparatus side using the arm edge 42 as a groundterminal, and the ground resistance [Ω] including the arm member 40, thecartridge body 53, and the cassette compartment 31 is in the order of10⁷ or less.

Accordingly, the magnetic tape 6 is connected through the arm member 40and cartridge body 53 to the cassette compartment 31 electricallygrounded, and therefore the magnetic surface 6M of the magnetic tape 6is prevented from being charged, and, even when being charged, chargescan be surely drained through the arm member 40 and cartridge body 53toward the external ground circuit E2 including the cassette compartment31, so that attack to the magnetic head due to charges on the magneticsurface 6M of the magnetic tape 6 is prevented, thus making it possibleto avoid electrostatic discharge damage of the magnetic head. Especiallyin the recording/reproducing apparatus having as a magnetic head an MRhead which is very easily affected by static charge, the presentinvention is effective.

THIRD EMBODIMENT

FIG. 10 shows a magnetic tape cartridge C3 according to a thirdembodiment of the present invention. In the figure for the thirdembodiment and those for the above second embodiment, similar parts orportions are indicated by similar reference numerals and the detaileddescriptions therefore are omitted.

In the present embodiment, the back surface 6B of the magnetic tape 6 iselectrically grounded using a conductive arm member 43. An arm edge 43aof the arm member 43 has an elastic contact with the back surface 6B ofthe magnetic tape 6 wound round the tape reel 7 at a predeterminedelastic force F in the direction of the diameter. The arm member 43 isformed so as to have such a length that the arm edge 43 a can be incontact with the reel hub 7A of the tape reel 7, so that the arm edge 43a can be constantly in elastic contact with the back surface 6B of themagnetic tape 6 according to the reduction of the winding diameter ofthe magnetic tape 6.

In the present embodiment, the formulation of the back coat layer 24 isadjusted so that the surface resistivity [Ω/sq] of the back surface 6Bof the magnetic tape 6 becomes in the order of 10⁷ or less.

In the present embodiment, the back surface 6B of the magnetic tape 6 isprevented from being charged, and, even when being charged, charges canbe surely drained through the arm member 43 and cartridge body 53 towardthe external ground circuit E2 including the cassette compartment 31.

FORTH EMBODIMENT

FIG. 11 and FIG. 12 show a forth embodiment of the present invention. Inthe figures for the forth embodiment and those for the above first andsecond embodiments, similar parts or portions are indicated bysimilarreference numerals, and the detailed descriptions therefore are omitted.

The present embodiment is different from the above embodiments in that arecording/reproducing apparatus D for recording and reproducing amagnetic tape cartridge C4 prevents the magnetic tape 6 from beingcharged.

As the recording/reproducing apparatus D, a recording/reproducingapparatus of a front face insert type such that the magnetic tapecartridge C4 is inserted in the direction indicated by an arrow a fromthe side of the front face 3 a in which the switching door 18 is formedas shown in FIG. 11 is used. The magnetic tape cartridge C4 is set inthe inside cassette compartment 31 through the cartridge insert hole 32formed in a front panel 37 of the recording/reproducing apparatus D.

In the magnetic tape cartridge C4 set in the cassette compartment 31,the magnetic tape 6 is drawn by means of a tape drawing means throughthe opened switching door 18 and taken up by a take-up reel 45constituted by a metal material in the recording/reproducing apparatusD. In the tape path between the magnetic tape cartridge C4 and thetake-up reel 45, a plurality of guide rollers 47 a, 47 b, 47 c, 47 d, 47e, 47 f constituted by a metal are provided, and, as diagrammaticallyshown in FIG. 12, the traveling magnetic tape 6 is guided by the guiderollers 47 a to 47 f. A magnetic head 46 for recording information onthe magnetic tape 6 or reproducing information recorded on the magnetictape 6 is disposed between the guide roller 47 c and the guide roller 47d.

In the present embodiment, the surface resistivity [Ω/sq] of each of themagnetic surface 6M and the back surface 6B of the magnetic tape 6 is inthe order of 10⁷ or less. In addition, among the plurality of guiderollers 47 a to 47 f, the guide rollers 47 c, 47 d disposed immediatelybehind and immediately ahead of the magnetic head 46 as viewed in thetraveling direction of the magnetic tape 6 (having the magnetic head 46disposed therebetween) are individually connected to a ground circuit E4on the recording/reproducing apparatus D side. In this case, the groundresistance [Ω] using the guide rollers 47 c, 47 d as ground terminals isin the order of 10⁷ or less.

In the present embodiment, in the course of which the magnetic tape 6 inthe magnetic tape cartridge C4 set in the recording/reproducingapparatus D is taken up by the take-up reel 45, the back surface 6B ofthe magnetic tape 6 is in contact with the guide roller 47 c and guideroller 47 d, and therefore the back surface 6B of the magnetic tape 6 isprevented from being charged, so that the effect similar to that of theabove first embodiment can be obtained.

In the construction described above, the back surface 6B of the magnetictape 6 is brought into contact with the guide rollers 47 c, 47 d, but,for example, as shown in FIG. 13A, when the magnetic surface 6M of themagnetic tape 6 is guided by the guide rollers 47 c, 47 d connected tothe ground circuit E4, the magnetic surface 6M is prevented from beingcharged, thus making it possible to avoid electrostatic discharge damageof the magnetic head 46. Especially in the recording/reproducingapparatus having as a magnetic head an MR head which is very easilyaffected by static charge, this is effective.

In addition, FIG. 13B is an example of the construction in which theguide roller 47 c is disposed for the magnetic surface 6M of themagnetic tape 6 and the guide roller 47 d is disposed for the backsurface 6B of the magnetic tape 6. Further, FIG. 13C is an example ofthe construction in which the guide roller 47 c is disposed for the backsurface 6B of the magnetic tape 6 and the guide roller 47 d is disposedfor the magnetic surface 6M of the magnetic tape 6.

EXAMPLES

Herein below, Examples according to the preferred embodiments of thepresent invention will be described. In the following examples, theground effect of the magnetic tapes in the modes described above in thefirst to forth embodiments was examined. Examples 1 to 4 correspond tothe above-described construction of the first embodiment. Examples 5 to8 correspond to the second and third embodiments, and Examples 9 to 12correspond to the forth embodiment.

Example 1

On one surface of a polyethylene terephthalate (PET) film having athickness of 6.5 μm, a 0.1 μm metallic aluminum film was formed by avacuum deposition method, and a magnetic film having the formulationshown below was formed on the metallic aluminum film so as to have athickness of 0.2 μ. On another surface of the PET film, as a back coatlayer, a carbon black film included mainly of “KETJENBLACK” (tradename), manufactured and sold by Eastman Chemical Company, was formed soas to have a thickness of 0.7 μm.

Thus, there was prepared a magnetic tape 6 having a thickness of 7.5 μm,in which the surface resistivity of a magnetic surface 6M was 10E8 (10⁸)Ω/sq, and the surface resistivity of a back surface 6B was 10E7 Ω/sq orless.

The formulation of the magnetic layer is as follows. <Formulation of thecomposition for magnetic layer > Ferromagnetic fine powder 100 Parts byweight  (major axis length: 0.15 μm): Polyester polyurethane resin: 10Parts by weight (manufactured and sold by TOYOBO CO., LTD.; trade name:UR8200) Vinyl chloride copolymer: 10 Parts by weight (manufactured andsold by Nippon Zeon Co., Ltd.; trade name: MR110) Butyl stearate: 1 Partby weight Methyl ethyl ketone: 20 Parts by weight Toluene: 20 Parts byweight Cyclohexanone: 10 Parts by weight Alumina powder: 10 Parts byweight (manufactured and sold by Sumitomo Chemical Co., Ltd.; tradename: AKP50)

A mixture having the above formulation of the composition for magneticlayer was kneaded by means of a continuous kneader, and then dispersedusing a sand mill. Then, the resultant mixture was subjected tofiltration by means of a filter having an average pore size of 1 μm toprepare a composition for magnetic layer. The composition was applied tothe metallic aluminum film on the above PET film, and dried andcalendered to form a magnetic layer in the present Example.

As mentioned above, in the magnetic tape 6 having the construction shownin FIG. 4, the surface resistivity on the magnetic surface 6M side wasadjusted to be 10E8 Ω/sq, and the surface resistivity on the backsurface 6B side was adjusted to be 10E7 Ω/sq or less. Then, the reel hub7A (made of a metal or a conductive plastic; electric resistance: 10E7 Ωor less) of the magnetic tape cartridge C1 described in the firstembodiment was connected to the ground circuit E1 as shown in FIG. 6,and an antistatic effect for the magnetic tape was evaluated under theconditions for examination shown below (Examples 1-1 to 1-18).

The evaluation was made by observation of damage of the magnetic headusing an MR element. In the examination, a recording/reproducingapparatus, DLT7000 (model name), manufactured and sold by Quantum Corp.,was used. It is noted that the magnetic head was replaced by a magnetichead (AMR head) used in “DCR-IP7”, manufactured and sold by SonyCorporation, which was processed so that it could be mounted on theDLT7000. The number of loops of the magnetic tape (frequency of thecycles of from the start of feeding the tape to the completion ofwinding) was individually set at 100, 200, 500, and 1,000, and theeffect of static charge caused by the increase of the tape travelinglength was also evaluated.

The results of the evaluations are shown in Table 1, together with theresults of the Comparative Examples under the conditions shown below. InTable 1, symbol “ο” means that the magnetic head suffered no damage,that is, electrostatic discharge of the magnetic tape was satisfactorilyprevented. Symbol “Δ” means that the magnetic head deteriorated due toelectrostatic discharge which occurred between the magnetic head and themagnetic tape, and symbol “X” means that the MR element constituting themagnetic head was broken due to electrostatic discharge to form a holethrough the element. The operating environment (conditions oftemperature and humidity) was at 5° C./10% RH (relative humidity). TABLE1 AMR head (5° C./10% RH) Number of loops Up to Up to 100 Up to 200 Upto 500 1,000 Example loops loops loops loops Example 1-1 ◯ ◯ ◯ ◯ 1-2 ◯ ◯◯ ◯ 1-3 ◯ ◯ ◯ ◯ 1-4 ◯ ◯ ◯ ◯ 1-5 ◯ ◯ ◯ ◯ 1-6 ◯ ◯ ◯ ◯ 1-7 ◯ ◯ ◯ ◯ 1-8 ◯ ◯◯ ◯ 1-9 ◯ ◯ ◯ ◯ 1-10 ◯ ◯ ◯ ◯ 1-11 ◯ ◯ ◯ ◯ 1-12 ◯ ◯ ◯ ◯ 1-13 ◯ ◯ ◯ ◯ 1-14◯ ◯ ◯ ◯ 1-15 ◯ ◯ ◯ ◯ 1-16 ◯ ◯ ◯ ◯ 1-17 ◯ ◯ ◯ ◯ 1-18 ◯ ◯ ◯ ◯ Comparative1-1 ◯ X X X Example 1-2 ◯ X X X 1-3 ◯ ◯ ◯ Δ

Example 1-1

The magnetic layer 23 at each of the leader (end portion on the side ofthe leader tape 9; this applies to the following) and the trailer (endportion on the side of the reel hub 7A of the tape reel 7; this appliesto the following) of the magnetic tape 6 was completely peeled off toexpose the underlying nonmagnetic conductor layer 22, and thenonmagnetic conductor layer 22 on the leader side was directly broughtinto contact (not through the leader tape 9 but using, for example, anadhesive tape; this applies to the following) with a reel hub of thegrounded take-up reel made of a metal in the recording/reproducingapparatus, and the nonmagnetic conductor layer on the trailer side wasbrought into contact the reel hub 7A made of a metal in the mode shownin FIG. 5 (A) (each contact resistance: 10E2 Ω or less).

The reason why the tape leader side was directly brought into contactwith the reel hub of the take-up reel resides in that the leader tape 9is generally constituted by a nonconductive material, such as PET. Whenthe leader tape 9 is constituted by a conductive material, such as analuminum alloy, the leader tape is not required to be directly broughtinto contact with the reel hub using an adhesive tape as mentionedabove. The range of the magnetic layer 23 to be removed is a range suchthat the underlying nonmagnetic conductor layer 22 can be surely incontact with the reel hub, and, in the present Example, it was a portionof the magnetic tape about 5 mm from each of the tape leader and thetape trailer in the longitudinal direction of the tape (this applies tothe following).

The results of the examinations can confirm that the magnetic tape 6 isprevented from being charged so that the magnetic head suffers nodamage. The reason for this is presumed that the nonmagnetic conductorlayer 22 having a lower resistance is electrically connected directly tothe reel hub 7A of the tape reel 7 and the reel hub of the take-up reel,and hence charges on the magnetic tape 6 can escape through theindividual reel hubs, thus preventing discharge on the magnetic head.

Example 1-2

The back surface 6B on the leader side of the magnetic tape was directlybrought into contact with the reel hub of the grounded take-up reel madeof a metal in the recording/reproducing apparatus, and the back surface6B on the trailer side was brought into contact with the reel hub 7Amade of a metal in the mode shown in FIG. 5(B).

The results of the examinations can confirm that the magnetic tape 6 isprevented from being charged so that the magnetic head suffers nodamage. From this, it is found that, when the back surface 6Belectrically connected to the reel hub 7A of the tape reel 7 and thereel hub of the take-up reel has a surface resistivity of 10E7 Ω/sq orless, the magnetic tape 6 is prevented from being charged.

The magnetic head does not face the back surface but the magneticsurface, and therefore a construction such that the magnetic surface ofthe tape is prevented from being charged is inherently needed. However,in the present Example, the construction in which the back surface ofthe tape is prevented from being charged provides optimum results. Thereason for this is presumed that, in the magnetic tape wound round theindividual reel hubs of the tape reel 7 and the take-up reel, themagnetic surface on the inner side and the back surface on the outerside are in contact with each other, and therefore charges on themagnetic surface escape through the back surface toward the individualreel hubs.

Example 1-3

The magnetic layer 23 only on the leader side of the magnetic tape wascompletely peeled off to expose the underlying nonmagnetic conductorlayer 22 and the nonmagnetic conductor layer 22 on the leader side wasdirectly brought into contact with the reel hub of the grounded take-upreel made of a metal in the recording/reproducing apparatus, and themagnetic surface 6M on the tape trailer side was brought into contactwith the reel hub 7A made of a metal.

The results of the examinations can confirm that the magnetic tape 6 isprevented from being charged so that the magnetic head suffers nodamage. From the results, it is impossible to specify as to whether theground effect of the nonmagnetic conductor layer 22 on the tape leaderside connected to the reel hub of the take-up reel is effective or theground effect of the magnetic surface 6M (magnetic layer 23) on the tapetrailer side connected to the reel hub 7A of the tape reel 7 iseffective, but it is presumed that the nonmagnetic conductor layer 22having a resistance lower than that of the magnetic surface 6M isgrounded to prevent the magnetic tape from being charged.

Example 1-4

The back surface 6B on the leader side of the magnetic tape was directlybrought into contact with the reel hub of the grounded take-up reel madeof a metal in the recording/reproducing apparatus, and the magneticsurface 6M on the tape trailer side was brought into contact with thereel hub 7A made of a metal.

The results of the examinations can confirm that the magnetic tape 6 isprevented from being charged so that the magnetic head suffers nodamage. From the results, it is impossible to specify as to whether theground effect of the back surface B on the tape leader side connected tothe reel hub of the take-up reel is effective or the ground effect ofthe magnetic surface 6M (magnetic layer 23) on the tape trailer sideconnected to the reel hub 7A of the tape reel 7 is effective, but it ispresumed that the back surface 6B having a resistance lower than that ofthe magnetic surface 6M is grounded to prevent the magnetic tape frombeing charged.

Example 1-5

The leader side of the magnetic tape was wound round the reel hub of thegrounded take-up reel made of a metal in the recording/reproducingapparatus through the leader tape (nonconductive leader tape; thisapplies to the following) 9, and the magnetic layer 23 only on the tapetrailer side was completely peeled off to expose the underlyingnonmagnetic conductor layer 22 and the exposed nonmagnetic conductorlayer 22 was brought into contact with the reel hub 7A made of a metalin the mode shown in FIG. 5(A).

The results of the examinations can confirm that the magnetic tape 6 isprevented from being charged so that the magnetic head suffers nodamage. From the results, it is found that, when the nonmagneticconductor layer 22 is grounded at least one end portion of the magnetictape 6, a satisfactory antistatic effect for the magnetic tape 6 can beobtained.

Example 1-6

The leader side of the magnetic tape was wound round the reel hub of thegrounded take-up reel made of a metal in the recording/reproducingapparatus through the leader tape 9, and the back surface 6B on the tapetrailer side was brought into contact with the reel hub 7A made of ametal in the mode shown in FIG. 5(B).

The results of the examinations can confirm that the magnetic tape 6 isprevented from being charged so that the magnetic head suffers nodamage. From the results, it is found that, when the back surface 6B isgrounded at least one end portion of the magnetic tape 6, a satisfactoryantistatic effect for the magnetic tape 6 can be obtained.

Example 1-7

The magnetic layer 23 at each of the leader and the trailer of themagnetic tape 6 was completely peeled off to expose the underlyingnonmagnetic conductor layer 22 and the nonmagnetic conductor layer 22 onthe leader side was directly brought into contact with the reel hub ofthe grounded take-up reel made of a metal in the recording/reproducingapparatus, and the nonmagnetic conductor layer 22 on the trailer sidewas brought into contact with the reel hub 7A made of a conductiveplastic (manufactured and sold by Mitsubishi Engineering-PlasticsCorporation; trade name: CF2010 antistatic grade; surface resistivity:about 6×10E6 Ω/sq) in the mode shown in FIG. 5(A). The results of theexaminations can confirm that the magnetic tape 6 is prevented frombeing charged so that the magnetic head suffers no damage.

Example 1-8

The back surface 6B on the leader side of the magnetic tape was directlybrought into contact with the reel hub of the grounded take-up reel madeof a metal in the recording/reproducing apparatus, and the back surface6B on the trailer side was brought into contact with the reel hub 7Amade of the above conductive plastic in the mode shown in FIG. 5(B). Theresults of the examinations can confirm that the magnetic tape 6 isprevented from being charged so that the magnetic head suffers nodamage.

Example 1-9

The magnetic layer 23 only on the leader side of the magnetic tape wascompletely peeled off to expose the underlying nonmagnetic conductorlayer 22 and the nonmagnetic conductor layer 22 on the leader side wasdirectly brought into contact with the reel hub of the grounded take-upreel made of a metal in the recording/reproducing apparatus, and themagnetic surface 6M on the tape trailer side was brought into contactwith the reel hub 7A made of the above conductive plastic. The resultsof the examinations can confirm that the magnetic tape 6 is preventedfrom being charged so that the magnetic head suffers no damage.

Example 1-10

The back surface 6B on the leader side of the magnetic tape was directlybrought into contact with the reel hub of the grounded take-up reel madeof a metal in the recording/reproducing apparatus, and the magneticsurface 6M on the tape trailer side was brought into contact with thereel hub 7A made of the above conductive plastic. The results of theexaminations can confirm that the magnetic tape 6 is prevented frombeing charged so that the magnetic head suffers no damage.

Example 1-11

The leader side of the magnetic tape was wound round the reel hub of thegrounded take-up reel made of a metal in the recording/reproducingapparatus through the leader tape 9, and the magnetic layer 23 only onthe tape trailer side was completely peeled off to expose the underlyingnonmagnetic conductor layer 22 and the exposed nonmagnetic conductorlayer 22 was brought into contact with the reel hub 7A made of the aboveconductive plastic in the mode shown in FIG. 5(A). The results of theexaminations can confirm that the magnetic tape 6 is prevented frombeing charged so that the magnetic head suffers no damage.

Example 1-12

The leader side of the magnetic tape was wound round the reel hub of thegrounded take-up reel made of a metal in the recording/reproducingapparatus through the leader tape 9, and the back surface 6B on the tapetrailer side was brought into contact with the reel hub 7A made of theabove conductive plastic in the mode shown in FIG. 5(B). The results ofthe examinations can confirm that the magnetic tape 6 is prevented frombeing charged so that the magnetic head suffers no damage.

From the results of the examinations in Examples 1-7 to 1-12, it isfound that, when the reel hub 7A as a ground terminal has a surfaceresistivity of about 6×10E6 Ω/sq, a satisfactory antistat effect for themagnetic tape 6 can be obtained.

Example 1-13

The magnetic layer 23 at each of the leader and the trailer of themagnetic tape 6 was incompletely removed so that the contact resistancebetween the magnetic tape and the reel hub of the grounded take-up reelmade of a metal in the recording/reproducing apparatus and the contactresistance between the magnetic tape and the reel hub 7A of the tapereel 7 individually became about 10E7 Ω, and the partially exposednonmagnetic conductor layers 22 were respectively brought into contactwith the reel hub of the take-up reel and the reel hub 7A of the tapereel 7.

The results of the examinations can confirm that the magnetic tape 6 isprevented from being charged so that the magnetic head suffers nodamage. From the results, it is found that, when the contact resistancebetween the reel hub of the take-up reel or the reel hub 7A of the tapereel 7 and the magnetic tape 6 is 10E7 Ω, a satisfactory antistaticeffect for the magnetic tape 6 can be obtained.

Example 1-14

The magnetic layer 23 only on the leader side of the magnetic tape 6 wasincompletely removed so that the contact resistance between the magnetictape and the reel hub of the grounded take-up reel made of a metal inthe recording/reproducing apparatus became about 10E7 Ω, and broughtinto contact with the reel hub, and the magnetic surface 6M on the tapetrailer side was brought into contact with the reel hub 7A made of ametal. The results of the examinations can confirm that the magnetictape 6 is prevented from being charged so that the magnetic head suffersno damage.

Example 1-15

The leader side of the magnetic tape 6 was brought into contact with thereel hub of the grounded take-up reel made of a metal in therecording/reproducing apparatus through the leader tape 9, and themagnetic layer 23 on the tape trailer side was incompletely removed sothat the contact resistance between the magnetic tape and the reel hub7A of the tape reel 7 became about 10E7 Ω, and brought into contact withthe reel hub 7A. The results of the examinations can confirm that themagnetic tape 6 is prevented from being charged so that the magnetichead suffers no damage.

Example 1-16

The magnetic layer 23 at each of the leader and the trailer of themagnetic tape 6 was incompletely removed so that the contact resistancebetween the magnetic tape and the reel hub of the grounded take-up reelmade of a metal in the recording/reproducing apparatus and the contactresistance between the magnetic tape and the reel hub 7A made of theabove conductive plastic of the tape reel 7 individually became about10E7 Ω, and the partially exposed nonmagnetic conductor layers 22 werebrought into contact with the respective reel hubs. The results of theexaminations can confirm that the magnetic tape 6 is prevented frombeing charged so that the magnetic head suffers no damage.

Example 1-17

The magnetic layer 23 only on the leader side of the magnetic tape wasincompletely removed so that the contact resistance between the magnetictape and the reel hub of the grounded take-up reel made of a metal inthe recording/reproducing apparatus became about 10E7 Ω, and thepartially exposed nonmagnetic conductor layer 22 was brought intocontact with the reel hub, and the magnetic surface 6M on the tapetrailer side was brought into contact with the reel hub 7A made of theabove conductive plastic. The results of the examinations can confirmthat the magnetic tape 6 is prevented from being charged so that themagnetic head suffers no damage.

Example 1-18

The leader side of the magnetic tape was wound round the reel hub of thegrounded take-up reel made of a metal in the recording/reproducingapparatus through the leader tape 9, and the magnetic layer 23 only onthe tape trailer side was incompletely removed so that the contactresistance between the magnetic tape and the reel hub 7A made of theabove conductive plastic of the tape reel 7 became about 10E7 Ω, and thepartially exposed nonmagnetic conductor layer 22 was brought intocontact with the reel hub 7A. The results of the examinations canconfirm that the magnetic tape 6 is prevented from being charged so thatthe magnetic head suffers no damage.

Comparative Example 1-1

The reel hub 7A of the tape reel 7 in Example 1-5 was formed from ageneral polycarbonate resin having no conductivity (in the presentexample, polycarbonate resin S2000, manufactured and sold by MitsubishiEngineering-Plastics Corporation; surface resistivity: 10E15 Ω/sq ormore) and grounded.

Comparative Example 1-2

The reel hub 7A of the tape reel 7 in Example 1-5 was formed from theabove polycarbonate resin and was not grounded.

The results of the Comparative Examples 1-1 and 1-2 can confirm that,especially when the number of loops exceeds 100, the magnetic headsuffers damage due to electrostatic discharge on the magnetic tape 6,irrespective of whether the reel hub 7A is grounded or not grounded.

Comparative Example 1-3

The surface resistivity of each of the reel hub of the take-up reel andthe reel hub 7A of the tape reel 7 in Example 1-1 was 10E8 Ω/sq. Theresults of the examinations can confirm that a relatively optimumantistatic effect for the magnetic tape 6 is recognized, but, when thenumber of loops exceeds 500, the magnetic head suffers damage due toelectrostatic discharge on the magnetic tape 6.

From the Table 1 above, it is found that, when at least one end portionof the leader and the trailer of the magnetic tape 6 are electricallygrounded, deterioration or electrostatic discharge damage of themagnetic head is prevented. In this case, the grounded surface of themagnetic tape 6 may be any of the magnetic surface 6M side and the backsurface 6B side, and the reel hub 7A may be made of any of a metal and aconductive plastic.

However, as can be seen in the results of Examples 1-13 to -18 andComparative Example 1-3, from the viewpoint of achieving optimumreliability, it is preferred that the contact resistance between themagnetic tape 6 and the reel hub 7A and the ground resistance of theground circuit using the reel hub 7A as a ground terminal areindividually 10E7 Ω or less. In other words, the amount of charges onthe magnetic tape is increased as the traveling distance of the magnetictape 6 increases, and the present Examples can confirm that, forpreventing the charges from causing discharge on the magnetic head, aconstruction is very effective in which the connection end portion ofthe magnetic tape 6 on the reel hub 7A side has a surface resistivity[Ω/sq] in the order of 10⁷ or less so that the charges escape throughthe conductive reel hub 7A.

In addition, it is presumed that, when the magnetic surface 6M of themagnetic tape 6 has a surface resistivity [Ω/sq] in the order of 10⁷ orless, there is no need to remove the magnetic layer 23 and bring thenonmagnetic conductor layer 22 having a lower resistance into contactwith the reel hub 7A. This is considered to suggest that, when thesurface resistivity of the magnetic surface 6M in the magnetic tape 6having the above construction exceeds the value in the order of 10⁷, theunderlying nonmagnetic conductor layer 22 should be connected to thereel hub, and, when the surface resistivity is in the order of 10⁷ orless, the nonmagnetic conductor layer should be directly (through themagnetic layer 23) connected to the reel hub 7A.

Example 2

As a magnetic head for the recording/reproducing apparatus used in theexaminations in Example 1, one obtained by processing the GMR headhaving the element structure diagrammatically shown in FIG. 14 so thatit could be mounted on DLT7000, manufactured and sold by Quantum Corp.,was used to confirm the ground effect of the magnetic tape 6.

The element structure of the GMR head used in the examinations isconstituted by, as shown in FIG. 14, forming an upper shielding layer(NiFe) 61 having a thickness of 2 to 3 μm and a lower shielding layer(NiFe) 62 having a thickness of 2 to 3 μm at a gap of 160 nm, andstacking on one another a Ta layer (5.0 nm) 63, a PtMn layer (30.0 nm)64, a CoFe layer (2.2 nm) 65, a Cu layer (2.9 nm) 66, a CoFe layer (2.0nm) 67, a NiFe layer (6.0 nm) 68, and a Ta layer (5.0 nm) 69 from theupper shielding layer 61 side. A gap G1 between the upper shieldinglayer 61 and the opposite Ta layer 63 is 37.9 nm and a gap G2 betweenthe lower shielding layer 62 and the opposite Ta layer 69 is 69.0 nm,and the gaps G1, G2 are filled with an electrically insulating material,such as Al₂O_(3 or SiO) _(2.)

The PtMn layer 64 as a non-ferromagnetic layer locks the direction ofmagnetization of the CoFe layer 65 as a so-called locked MR layer in afixed direction. The direction of magnetization of the CoFe layer 67 andNiFe layer 68 as a so-called free MR layer freely rotates in thepresence of an external magnetic field (magnetic field of the signalrecorded on the magnetic recording medium). The GMR head has a basicprinciple such that a resistance change of the element (GMR effect),which is proportional to the cosine of an angle α between the directionof magnetization of the locked MR layers and the direction ofmagnetization of the free MR layer, is read to output a signal forreproduction.

The AMR head has a basic structure corresponding to the construction ofelement structure of the GMR head in which the locked MR layer isomitted. The AMR head has a basic principle different from the principleof reproduction of the GMR head in that a resistance change of theelement (AMR effect), which is proportional to the cosine of an angle βbetween the direction of a sense current flowing the free MR layer andthe direction of magnetization of the free MR layer, is read to output asignal for reproduction.

Electrostatic discharge damage of the GMR head is caused byelectrostatic charges on the magnetic tape, which penetrate the gap (G1,G2) to undergo discharge on the element. Generally, the thickness of theGMR element is as small as 0.1 to 0.3 μm, as compared to the thickness(0.5 to 1.0 μm) of the AMR element. Therefore, the GMR element maysuffer damage even at a static voltage such that the element in the AMRhead suffers no damage.

The present Examples are important for confirming whether or not thepresent invention is effective in the MR head using the GMR elementwhich is very sensitive to static charge as mentioned above. Theconditions for examination in the present Examples (Examples 2-1 to 2-18and Comparative Examples 2-1 to 2-3) correspond to those in the aboveExamples 1-1 to 1-18 and Comparative Examples 1-1 to 1-3, respectively.The results of the evaluations are shown in Table 2. TABLE 2 GMR head(5° C./10% RH) Number of loops Up to Up to 100 Up to 200 Up to 500 1,000Example loops loops loops loops Example 2-1 ◯ ◯ ◯ ◯ 2-2 ◯ ◯ ◯ ◯ 2-3 ◯ ◯◯ ◯ 2-4 ◯ ◯ ◯ ◯ 2-5 ◯ ◯ ◯ ◯ 2-6 ◯ ◯ ◯ ◯ 2-7 ◯ ◯ ◯ ◯ 2-8 ◯ ◯ ◯ ◯ 2-9 ◯ ◯◯ ◯ 2-10 ◯ ◯ ◯ ◯ 2-11 ◯ ◯ ◯ ◯ 2-12 ◯ ◯ ◯ ◯ 2-13 ◯ ◯ ◯ ◯ 2-14 ◯ ◯ ◯ ◯2-15 ◯ ◯ ◯ ◯ 2-16 ◯ ◯ ◯ ◯ 2-17 ◯ ◯ ◯ ◯ 2-18 ◯ ◯ ◯ ◯ Comparative 2-1 X XX X Example 2-2 X X X X 2-3 ◯ Δ Δ Δ

From Table 2, it is found that, even when the GMR element which is verysensitive to static charge is used in the magnetic head, damage of themagnetic head is avoided under the conditions for examination inExamples 2-1 to 2-18, and the effectiveness of the present invention canbe confirmed.

Example 3

The examination in Example 1 was conducted in an operating environmentunder conditions of temperature and humidity at 65° C./10% RH. Theconditions for examination below (Examples 3-1 to 3-18 and ComparativeExamples 3-1 to 3-3) correspond to those in the above Examples 1-1 to1-18 and Comparative Examples 1-1 to 1-3, respectively. The results ofthe evaluations are shown in Table 3. TABLE 3 AMR head (65° C./10% RH)Number of loops Up to Up to 100 Up to 200 Up to 500 1,000 Example loopsloops loops loops Example 3-1 ◯ ◯ ◯ ◯ 3-2 ◯ ◯ ◯ ◯ 3-3 ◯ ◯ ◯ ◯ 3-4 ◯ ◯ ◯◯ 3-5 ◯ ◯ ◯ ◯ 3-6 ◯ ◯ ◯ ◯ 3-7 ◯ ◯ ◯ ◯ 3-8 ◯ ◯ ◯ ◯ 3-9 ◯ ◯ ◯ ◯ 3-10 ◯ ◯ ◯◯ 3-11 ◯ ◯ ◯ ◯ 3-12 ◯ ◯ ◯ ◯ 3-13 ◯ ◯ ◯ ◯ 3-14 ◯ ◯ ◯ ◯ 3-15 ◯ ◯ ◯ ◯ 3-16◯ ◯ ◯ ◯ 3-17 ◯ ◯ ◯ ◯ 3-18 ◯ ◯ ◯ ◯ Comparative 3-1 ◯ X X X Example 3-2 ◯X X X 3-3 ◯ ◯ ◯ Δ

As can be seen in Table 3, in the present Examples, the resultscompletely similar to those in the Example 1 above were obtained. Thetemperature condition of 65° C. is close to the temperature at which themagnetic tape cartridge is actually used, and the effectiveness of thepresent invention can be confirmed even under the conditions at 65°C./10% RH, namely, at a high temperature and a low humidity.

Example 4

The magnetic head in Example 1 was constituted by the GMR elementdescribed with reference to FIG. 14, and the examination was conductedin an operating environment under conditions of temperature and humidityat 65° C./10% RH. The conditions for examination below (Examples 4-1 to4-18 and Comparative Examples 4-1 to 4-3) correspond to those in theabove Examples 1-1 to 1-18 and Comparative Examples 1-1 to 1-3,respectively. The results of the evaluations are shown in Table 4. TABLE4 GMR head (65° C./10% RH) Number of loops Up to Up to 100 Up to 200 Upto 500 1,000 Example loops loops loops loops Example 4-1 ◯ ◯ ◯ ◯ 4-2 ◯ ◯◯ ◯ 4-3 ◯ ◯ ◯ ◯ 4-4 ◯ ◯ ◯ ◯ 4-5 ◯ ◯ ◯ ◯ 4-6 ◯ ◯ ◯ ◯ 4-7 ◯ ◯ ◯ ◯ 4-8 ◯ ◯◯ ◯ 4-9 ◯ ◯ ◯ ◯ 4-10 ◯ ◯ ◯ ◯ 4-11 ◯ ◯ ◯ ◯ 4-12 ◯ ◯ ◯ ◯ 4-13 ◯ ◯ ◯ ◯ 4-14◯ ◯ ◯ ◯ 4-15 ◯ ◯ ◯ ◯ 4-16 ◯ ◯ ◯ ◯ 4-17 ◯ ◯ ◯ ◯ 4-18 ◯ ◯ ◯ ◯ Comparative4-1 Δ X X X Example 4-2 X X X X 4-3 ◯ Δ Δ Δ

As can be seen in Table 4, in the present Examples, the resultssubstantially similar to those in the Example 2 above were obtained. Theresult of Comparative Example 2-1 is “X”, whereas the result ofComparative Example 4-1 is “Δ”, and the reason for this is presumed toreside in a difference in the conditions for examination of temperatureand humidity between 5° C./10% RH (Comparative Example 2-1) and 65°C./10% RH (Comparative Example 4-1). Specifically, taking intoconsideration the fact that the absolute humidity is likely to be highas the temperature rises even when the relative humidity is fixed, it ispresumed that the conditions for examination in Comparative Example 4-1,which are at a high humidity, as compared to those in ComparativeExample 2-1, suppress electrostatic discharge, although that is at anunsatisfactory level.

From the results of the Examples 1 to 4 above, there can be obtainedfindings that, for avoiding electrostatic discharge damage of themagnetic head, it is necessary that the surface resistivity [Ω/sq] ofeach of the magnetic surface 6M and the back surface 6B of the magnetictape 6 be in the order of 10⁷ or less. In the following Examples 5 to12, a magnetic tape having the below-described construction wasprepared, and examinations for evaluation of the antistatic effect forthe magnetic tape in the construction corresponding to the above secondto forth embodiments were conducted.

Example 5

On one surface of a polyethylene terephthalate (PET) film having athickness of 6.5 μm, a 0.1 μm metallic aluminum film was formed by avacuum deposition method, and a magnetic film having the formulationshown below was formed on the metallic aluminum film so as to have athickness of 0.2 μm. On another surface of the PET film, as a back coatlayer, a carbon black film included mainly of KETJENBLACK (trade name),manufactured and sold by Eastman Chemical Company, was formed so as tohave a thickness of 0.7 μm. Thus, there was prepared a magnetic tapehaving a thickness of 7.5 μm, in which the surface resistivity of themagnetic surface was 10E6 Ω/sq, and the surface resistivity of the backsurface was 10E7 Ω/sq or less (hereinafter, referred to as “magnetictape having the basic construction”).

The formulation of the magnetic layer is as follows. <Formulation of thecomposition for magnetic layer > Ferromagnetic fine powder 100 Parts byweight  (major axis length: 0.15 μm): Polyester polyurethane resin:  7Parts by weight (manufactured and sold by TOYOBO CO., LTD.; trade name:UR8200) Vinyl chloride copolymer:  8 Parts by weight (manufactured andsold by Nippon Zeon Co., Ltd.; trade name: MR110) Stearic acid: 1 Partby weight Butyl stearate:  2 Parts by weight Methyl ethyl ketone: 20Parts by weight Toluene: 20 Parts by weight Cyclohexanone: 10 Parts byweight Alumina powder: 10 Parts by weight (manufactured and sold bySumitomo Chemical Co., Ltd.; trade name: AKP50)

A mixture having the above formulation of the composition for magneticlayer was kneaded by means of a continuous kneader, and then dispersedusing a sand mill. Then, the resultant mixture was subjected tofiltration by means of a filter having an average pore size of 1 μm toprepare a composition for magnetic layer. The composition was applied tothe metallic aluminum film on the above PET film, and dried andcalendered to form a magnetic layer in the present Example.

The magnetic tape having the above basic construction was applied to themagnetic tape 6 of the magnetic tape cartridge C2 in the second andthird embodiments, and the cartridge body 53 was constituted by aconductive plastic (manufactured and sold by MitsubishiEngineering-Plastics Corporation; trade name: “CF2010 antistatic grade”;surface resistivity: about 6×10E6 Ω/sq). Then, the arm member 40 (43)made of a metal or the above conductive plastic was disposed between theinner wall of the cartridge body 53 and the magnetic tape 6, and broughtinto contact with the magnetic surface 6M or back surface 6B of themagnetic tape 6 at a pressure of about 0.5 to 2.5 g (contact resistance:10E7 Ω or less) to ground the magnetic tape 6.

The results of the examinations conducted under the conditions forexamination shown below (Examples 5-1 to 5-4 and Comparative Examples5-1 and 5-2) are shown in Table 5. The conditions of temperature andhumidity were at 5° C./10% RH, and the recording/reproducing apparatuswas the same as the apparatus (using an AMR head as a magnetic head)used in Example 1. TABLE 5 AMR head (5° C./10% RH) Number of loops Up toUp to 100 Up to 200 Up to 500 1,000 Example loops loops loops loopsExample 5-1 ◯ ◯ ◯ ◯ 5-2 ◯ ◯ ◯ ◯ 5-3 ◯ ◯ ◯ ◯ 5-4 ◯ ◯ ◯ ◯ ComparativeExample X X X X 5-1 Comparative Example X X X X 5-2

Example 5-1

The arm member 40 was formed from an aluminum alloy, and the edge 42 ofthe arm member 40 was brought into contact with the magnetic surface 6Mof the magnetic tape 6 in the mode shown in FIG. 7. The results of theexaminations can confirm that the magnetic tape 6 is prevented frombeing charged so that the magnetic head suffers no damage.

Example 5-2

The arm member 43 was formed from an aluminum alloy, and the edge 43 aof the arm member 43 was brought into contact with the back surface 6Bof the magnetic tape 6 in the mode shown in FIG. 10. The results of theexaminations can confirm that the magnetic tape 6 is prevented frombeing charged so that the magnetic head suffers no damage.

Example 5-3

The arm member 40 was formed from the above conductive plastic, and theedge 42 of the arm member 40 was brought into contact with the magneticsurface 6M of the magnetic tape 6 in the mode shown in FIG. 7. Theresults of the examinations can confirm that the magnetic tape 6 isprevented from being charged so that the magnetic head suffers nodamage.

Example 5-4

The arm member 43 was formed from the above conductive plastic, and theedge 43 a of the arm member 43 was brought into contact with the backsurface 6B of the magnetic tape 6 in the mode shown in FIG. 10. Theresults of the examinations can confirm that the magnetic tape 6 isprevented from being charged so that the magnetic head suffers nodamage.

Comparative Example 5-1

The arm member was formed from a polycarbonate resin having noconductivity (in the present example, S2000, manufactured and sold byMitsubishi Engineering-Plastics Corporation; surface resistivity: 10¹⁵Ω/sq or more), and the edge of the arm member was brought into contactwith the magnetic surface 6M of the magnetic tape 6 in the mode shown inFIG. 7.

Comparative Example 5-2

The arm member was formed from the above polycarbonate resin having noconductivity, and the edge of the arm member was brought into contactwith the back surface 6B of the magnetic tape 6 in the mode shown inFIG. 10.

From Table 5, it is found that deterioration or electrostatic dischargedamage of the magnetic head is prevented as long as the arm member hasconductivity. In this case, the contact surface of the magnetic tape 6to the arm member 40 or 43 may be any of the magnetic surface 6M sideand the back surface 6B side, and the material for the arm members 40,43 may be any of a metal and a conductive plastic.

Example 6

The magnetic head in Example 5 was constituted by the GMR elementdescribed with reference to FIG. 14 and the examination was conducted.The conditions for examination (Examples 6-1 to 6-4 and ComparativeExamples 6-1 and 6-2) correspond to those in the above Examples 5-1 to5-4 and Comparative Examples 5-1 and 5-2, respectively. The results ofthe examinations are shown in Table 6. TABLE 6 GMR head (5° C./10% RH)Number of loops Up to Up to 100 Up to 200 Up to 500 1,000 Example loopsloops loops loops Example 6-1 ◯ ◯ ◯ ◯ 6-2 ◯ ◯ ◯ ◯ 6-3 ◯ ◯ ◯ ◯ 6-4 ◯ ◯ ◯◯ Comparative Example X X X X 6-1 Comparative Example X X X X 6-2

From Table 6, it is found that the results similar to those in theExample 5 above are obtained. That is, even when the GMR element whichis very sensitive to static charge is used in the magnetic head, theeffectiveness of the present invention can be confirmed.

Example 7

The examination in Example 5 was conducted in an operating environmentunder conditions of temperature and humidity at 65° C./10% RH. Theconditions for examination (Examples 7-1 to 7-4 and Comparative Examples7-1 and 7-2) correspond to those in the above Examples 5-1 to 5-4 andComparative Examples 5-1 and 5-2, respectively. The results of theexaminations are shown in Table 7. TABLE 7 AMR head (65° C./10% RH)Number of loops Up to Up to 100 Up to 200 Up to 500 1,000 Example loopsloops loops loops Example 7-1 ◯ ◯ ◯ ◯ 7-2 ◯ ◯ ◯ ◯ 7-3 ◯ ◯ ◯ ◯ 7-4 ◯ ◯ ◯◯ Comparative Example X X X X 7-1 Comparative Example X X X X 7-2

Example 8

The magnetic head in Example 5 was constituted by the GMR elementdescribed with reference to FIG. 14, and the examination was conductedin an operating environment under conditions of temperature and humidityat 65° C./10% RH. The conditions for examination (Examples 8-1 to 8-4and Comparative Examples 8-1 and 8-2) correspond to those in the aboveExamples 5-1 to 5-4 and Comparative Examples 5-1 and 5-2, respectively.The results of the examinations are shown in Table 8. TABLE 8 GMR head(65° C./10%) Number of loops Up to Up to 100 Up to 200 Up to 500 1,000Example loops loops loops loops Example 8-1 ◯ ◯ ◯ ◯ 8-2 ◯ ◯ ◯ ◯ 8-3 ◯ ◯◯ ◯ 8-4 ◯ ◯ ◯ ◯ Comparative Example X X X X 8-1 Comparative Example X XX X 8-2

Example 9

Like the above forth embodiment (FIG. 12), among the plurality of guiderollers 47 a to 47 f used in the tape traveling system of therecording/reproducing apparatus D, the guide roller 47 c, 47 d disposedimmediately behind and/or immediately ahead of the magnetic head 46 wasgrounded. The magnetic tape having the above basic construction wasapplied to the magnetic tape 6 in the magnetic tape cartridge C4 toconfirm the antistatic effect for the magnetic tape 6. The conditions oftemperature and humidity were at 5° C./10% RH, and therecording/reproducing apparatus was the same as the apparatus (using anAMR head as a magnetic head) used in Example 1. The results of theexaminations conducted under the conditions for examination shown below(Examples 9-1 to 9-6 and Comparative Example 9) are shown in Table 9.TABLE 9 AMR head (5° C./10% RH) Number of loops Up to Up to 100 Up to200 Up to 500 1,000 Example loops loops loops loops Example 9-1 ◯ ◯ ◯ ◯9-2 ◯ ◯ ◯ ◯ 9-3 ◯ ◯ ◯ ◯ 9-4 ◯ ◯ ◯ ◯ 9-5 ◯ ◯ ◯ ◯ 9-6 ◯ ◯ ◯ ◯ Comparative◯ ◯ Δ X Example 9

Example 9-1

The guide rollers 47 c, 47 d immediately behind and immediately ahead ofthe magnetic head 46 (as viewed in the traveling direction of the tape;this applies to the following) were grounded, and the magnetic tape wasallowed to travel so that the magnetic surface 6M of the magnetic tape 6was in contact with the guide rollers 47 c, 47 d as shown in FIG. 13A.The results of the examinations can confirm that the magnetic tape 6 isprevented from being charged so that the magnetic head suffers nodamage.

Example 9-2

Only the guide roller 47 c immediately behind the magnetic head 46 inExample 9-1 was grounded. The results of the examinations can confirmthat the magnetic tape 6 is prevented from being charged so that themagnetic head suffers no damage.

Example 9-3

Only the guide roller 47 d immediately ahead of the magnetic head 46 inExample 9-1 was grounded. The results of the examinations can confirmthat the magnetic tape 6 is prevented from being charged so that themagnetic head suffers no damage.

Example 9-4

The guide rollers 47 c, 47 d immediately behind and immediately ahead ofthe magnetic head 46 were grounded, and the magnetic tape was allowed totravel so that the back surface 6B of the magnetic tape 6 was in contactwith the guide rollers 47 c, 47 d as shown in FIG. 12. The results ofthe examinations can confirm that the magnetic tape 6 is prevented frombeing charged so that the magnetic head suffers no damage.

Example 9-5

Only the guide roller 47 c immediately behind the magnetic head 46 inExample 9-4 was grounded. The results of the examinations can confirmthat the magnetic tape 6 is prevented from being charged so that themagnetic head suffers no damage.

Example 9-6

Only the guide roller 47 d immediately ahead of the magnetic head 46 inExample 9-4 was grounded. The results of the examinations can confirmthat the magnetic tape 6 is prevented from being charged so that themagnetic head suffers no damage.

Comparative Example 9

The guide rollers immediately behind and immediately ahead of themagnetic head were not grounded, and the magnetic tape was allowed totravel so that the magnetic surface of the magnetic tape was in contactwith the guide rollers (the guide rollers 47 c, 47 d in Example 9-1 werenot grounded).

From Table 9, the effectiveness of the present invention can beconfirmed, irrespective of whether the guide roller to be grounded isdisposed immediately behind or immediately ahead of the magnetic head,or whether the contact surface of the magnetic tape is the magneticsurface or the back surface.

Example 10

The magnetic head in Example 9 was constituted by the GMR elementdescribed with reference to FIG. 14 and the examination was conducted.The conditions for examination Examples 10-1 to 10-6 and ComparativeExample 10) correspond to those in the above Examples 9-1 to 9-6 andComparative Example 9, respectively. The results of the examinations areshown in Table 10. TABLE 10 GMR head (5° C./10% RH) Number of loops Upto Up to 100 Up to 200 Up to 500 1,000 Example loops loops loops loopsExample 10-1 ◯ ◯ ◯ ◯ 10-2 ◯ ◯ ◯ ◯ 10-3 ◯ ◯ ◯ ◯ 10-4 ◯ ◯ ◯ ◯ 10-5 ◯ ◯ ◯ ◯10-6 ◯ ◯ ◯ ◯ Comparative X X X X Example 10

From Table 10, it is found that the results similar to those in theExample 9 above are obtained. That is, even when the GMR element whichis very sensitive to static charge is used in the magnetic head, theeffectiveness of the present invention can be confirmed.

Example 11

The examination in Example 9 was conducted in an operating environmentunder conditions of temperature and humidity at 65° C./10% RH. Theconditions for examination (Examples 11-1 to 11-6 and ComparativeExample 11) correspond to those in the above Examples 9-1 to 9-6 andComparative Example 9, respectively. The results of the examinations areshown in Table 11. TABLE 11 AMR head (65° C./10% RH) Number of loops Upto Up to Up to Up to 100 200 500 1,000 Example loops loops loops loopsExample 11-1 ◯ ◯ ◯ ◯ 11-2 ◯ ◯ ◯ ◯ 11-3 ◯ ◯ ◯ ◯ 11-4 ◯ ◯ ◯ ◯ 11-5 ◯ ◯ ◯ ◯11-6 ◯ ◯ ◯ ◯ Comparative ◯ ◯ Δ X Example 11

Example 12

The magnetic head in Example 9 was constituted by the GMR elementdescribed with reference to FIG. 14, and the examination was conductedin an operating environment under conditions of temperature and humidityat 65° C./10% RH. The conditions for examination (Examples 12-1 to 12-6and Comparative Example 12) correspond to those in the above Examples9-1 to 9-6 and Comparative Example 9, respectively. The results of theexaminations are shown in Table 12. TABLE 12 GMR head (65° C./10% RH)Number of loops Up to Up to Up to Up to 100 200 500 1,000 Example loopsloops loops loops Example 12-1 ◯ ◯ ◯ ◯ 12-2 ◯ ◯ ◯ ◯ 12-3 ◯ ◯ ◯ ◯ 12-4 ◯◯ ◯ ◯ 12-5 ◯ ◯ ◯ ◯ 12-6 ◯ ◯ ◯ ◯ Comparative X X X X Example 12

Hereinabove, the embodiments of the present invention are individuallydescribed, but the present invention is not limited to theseembodiments, and can be changed or modified based on the technicalconcept of the present invention.

For example, in the above first embodiment, an explanation is made onthe construction in which the tape reel 7 (reel hub 7A) is formed from aconductive material, and electrically connected to the reel drive shaft33 on the recording/reproducing apparatus side during the tape loadingto ground the magnetic tape 6, but, instead of this, a construction maybe employed such that the cassette body 3 is constituted by a conductiveplastic, and the cassette body 3 is electrically connected to the tapereel 7 through the reel spring 8 made of a metal (see FIG. 6). In thisconstruction, the magnetic tape 6 is grounded during being used not onlythrough the reel drive shaft 33 but also by the sliding action of thecassette body 3 against the grounded cassette compartment on therecording/reproducing apparatus side, thus making it possible to preventthe magnetic head from suffering electrostatic discharge damage.

In addition, in the above second and third embodiments, the cassettebody 53 is constituted by a conductive plastic to make an electricalconnection between the arm members 40, 43 in contact with the magnetictape 6 and the cassette compartment 31, but, instead of this, aconstruction may be employed such that the cassette body 53 isconstituted by a general resin (having no conductivity) and, forexample, a base portion 40 a of the arm member 40 is disposed out of thecassette as shown in FIG. 15 so as to be directly in contact with thecassette compartment 31. The similar construction can be applied to thearm member 43.

Alternatively, the present invention can be applied to a constructionsuch that the electrical connection between the conductive cartridgebody 53 and the magnetic tape 6 or the conductive tape reel is made byproviding, for example, a conductive member, such as metallic wire ormetallic brush, on the inner wall of the cartridge or at the openingportion 34 for drawing the tape.

Further, in the above forth embodiment, among the plurality of guiderollers 47 a to 47 f constituting the tape traveling system of therecording/reproducing apparatus D, the guide roller 47 c and/or guideroller 47 d adjacent to the magnetic head is grounded, but theconstruction is not limited to this, and, in addition to the guiderollers 47 c, 47 d, or instead of the guide rollers 47 c, 47 d, anotherguide roller may be grounded.

Further, in the above embodiments, an explanation is made taking thesingle reel type magnetic tape cartridge as an example, but the magnetictape cartridge is not limited to this type, and the present inventioncan be applied to an LTO single reel type magnetic tape cartridge and amulti-reel type magnetic tape cartridge for DAT or 8 mm tape.

INDUSTRIAL APPLICABILITY

In the magnetic tape cartridge of the present invention, the reel hub isformed from a conductive material and one end portion of the magnetictape connected to the reel hub has a surface resistivity [Ω/sq] in theorder of 10⁷ or less. Therefore, charges on the magnetic tape aredrained through the reel hub toward, for example, therecording/reproducing apparatus side, thus making it possible to preventthe magnetic head from suffering damage due to electrostatic discharge.

In addition, in the magnetic tape cartridge of the present inventionwherein the cartridge body is formed from a conductive material, and themagnetic tape has surfaces individually having a surface resistivity[Ω/sq] in the order of 10⁷ or less and the magnetic tape is electricallyconnected to the cartridge body, charges on the magnetic tape aredrained through the cartridge body toward, for example, therecording/reproducing apparatus side, thus making it possible to preventthe magnetic head from suffering damage due to electrostatic discharge.

Further, in the apparatus for recording/reproducing a magnetic tapecartridge of the present invention, which apparatus includes at least amagnetic head for recording information on a magnetic tape orreproducing information recorded on the magnetic tape, and a pluralityof guide rollers for guiding the traveling magnetic tape, at least oneof the guide rollers is electrically grounded, and the traveling surfaceof the magnetic tape in contact with the grounded guide roller has asurface resistivity [Ω/sq] in the order of 10⁷ or less. Therefore,charges on the magnetic tape are drained through the grounded guideroller toward, for example, the recording/reproducing apparatus side,thus making it possible to prevent the magnetic head from sufferingdamage due to electrostatic discharge.

Furthermore, in each of the above constructions, when the magnetic tapeincludes a nonmagnetic conductor layer constituted by a nonmagneticconductive material disposed between a plastic film and a magneticlayer, the resistance of the magnetic tape can be lowered whilemaintaining optimum electromagnetic conversion properties of themagnetic layer in the magnetic tape.

1-12. (canceled)
 13. A magnetic tape cartridge comprising a reel hubhaving a magnetic tape wound there around, and a cartridge body forrotatably housing said reel hub, the magnetic tape cartridgecharacterized in that: said reel hub is formed by a conductive material;an end portion of said magnetic tape connected to said reel hub has asurface resistivity [Ω/sq] in the order of 10⁷ or less; and saidmagnetic tape comprises a nonmagnetic conductor layer including anonmagnetic conductive material disposed between a plastic film and amagnetic layer; wherein said end portion has said nonmagnetic conductorlayer exposed by removing said magnetic layer is electrically connectedto said reel hub; and said magnetic tape is connected to an externalground circuit including a reel drained axis electrically grounded viasaid reel hub.
 14. A magnetic tape cartridge comprising a reel hubhaving a magnetic tape wound there around, and a cartridge body forrotatably housing said reel hub, the magnetic tape cartridgecharacterized in that: said reel hub is formed by a conductive material;an end portion of said magnetic tape connected to said reel hub has asurface resistivity [Ω/sq] in the order of 10⁷ or less; said magnetictape has a back coat layer comprising a nonmagnetic conductive materialon a surface on an opposite side of a magnetic surface of said magnetictape; said end portion having said back coat layer electricallyconnected to said reel hub; and said magnetic tape is connected to anexternal ground circuit including a reel drained axis electricallygrounded via said reel hub.
 15. A magnetic tape cartridge comprising areel hub having a magnetic tape wound there around, and a cartridge bodyfor rotatably housing said reel hub, the magnetic tape cartridgecharacterized in that: said cartridge body is formed by a conductivematerial; surfaces of said magnetic tape have each a surface resistivity[Ω/sq] in the order of 10⁷ or less; said magnetic tape is electricallyconnected to said cartridge body; said cartridge body has providedtherein an arm member comprising a conductive material, wherein an endof said arm member is fixed to said cartridge body and another end is incontact with said magnetic tape; and said other end elastically contactssaid magnetic tape.
 16. The magnetic tape cartridge according to claim15, characterized in that said magnetic tape comprises a nonmagneticconductor layer having a nonmagnetic conductive material disposedbetween a plastic film and a magnetic layer; and said arm member is incontact with a magnetic surface of said magnetic tape.
 17. The magnetictape cartridge according to claim 15, characterized by having a backcoat layer comprising a nonmagnetic conductive material on a surface onan opposite side of a magnetic surface of said magnetic tape; and saidarm member is in contact said surface on the opposite side of saidmagnetic surface.
 18. A magnetic tape cartridge recording/reproducingapparatus comprising a reel hub having a magnetic tape wound therearound, and a cartridge body for rotatably housing said reel hub, themagnetic tape cartridge recording/reproducing apparatus characterizedby: at least a magnetic head for recording information on said magnetictape or reproducing information recorded on said magnetic tape, and aplurality of guide rollers for guiding said traveling magnetic tape;wherein at least one of said guide rollers disposed immediately in frontof and after said magnetic head is electrically grounded; a travelingsurface of said magnetic tape in contact with said grounded guide rollerhas a surface resistivity [Ω/sq] in the order of 10⁷ or less; saidmagnetic tape comprises a nonmagnetic conductor layer including anonmagnetic conductive material disposed between a plastic film and amagnetic layer; and said traveling surface of said magnetic tapecomprises said magnetic surface.
 19. A magnetic tape cartridgerecording/ reproducing apparatus comprising a reel hub having a magnetictape wound there around, and a cartridge body for rotatably housing saidreel hub, the magnetic tape cartridge recording/reproducing apparatuscharacterized by: at least a magnetic head for recording information onsaid magnetic tape or reproducing information recorded on said magnetictape, and a plurality of guide rollers for guiding said travelingmagnetic tape; wherein at least one of said guide rollers disposedimmediately in front of and after said magnetic heard is electricallygrounded; a traveling surface of said magnetic tape in contact with saidgrounded guide roller has a surface resistivity [Ω/sq] in the order of10⁷ or less; said magnetic tape has a back coat layer including anonmagnetic conductive material on a surface on a opposite side of amagnetic surface; and said traveling surface of said magnetic tapecomprises said surface on the opposite side of said magnetic surface.20. The magnetic tape cartridge recording/reproducing apparatusaccording to claim 18, characterized in that said magnetic headcomprises a magnetoresistive magnetic head.
 21. The magnetic tapecartridge recording/ reproducing apparatus according to claim 19,characterized in that said magnetic head comprises a magnetoresistivemagnetic head.
 22. The magnetic tape cartridge recording/reproducingapparatus according to claim 18, characterized in that said groundedguide roller comprises at least a pair of guide rollers having saidmagnetic head disposed therebetween.
 23. The magnetic tape cartridgerecording/reproducing apparatus according to claim 19, characterized inthat said grounded guide roller comprises at least a pair of guiderollers having said magnetic head disposed therebetween.